This invention relates to dental instruments and more particularly, is concerned with delivery units for dental delivery instruments. In a copending patent application (Ser. No. 150,050, filed May 15, 1980) there is disclosed a dental unit which holds a plurality of instruments in individual nests. The nests are moved to a storage position to an in-use position. Upon selection by the dentist the nest and the instrument it holds is moved from its storage position through an arcuate path of travel to place the instrument tangently onto the palm of the dentist.
Each nest is selected by switching a corresponding switch. Only one instrument is used at a time. The selection switches are grouped together and it is conceivable two or more switches may accidentally be switched either simultaneously or sequentally.
Accordingly, it is an object of this invention to provide means to assure that only one nest is extended to an in-use position. Another object of the invention is to provide means to increase the likelihood that the correct nest is extended in the presence of contradictory switching.